1. Technical Field
The present invention relates to a liquid discharging apparatus including a liquid discharging head configured to discharge liquid from nozzles in a transported discharged material, a carriage configured to mount the liquid discharging head and reciprocate in the direction intersecting the transport direction of the discharged material integrally with the liquid discharging head, and a carriage moving unit configured to cause the carriage to reciprocate.
In this specification, the term “liquid discharging apparatus” includes printing apparatuses including ink jet printers (serial printer) that execute printing jobs on a printed material by discharging ink from nozzles in a printhead, facsimile machines, and multifunctional peripherals, and apparatuses configured to discharge liquid corresponding to the application thereof instead of the ink from a liquid discharging head corresponding to the printhead onto a discharged material corresponding to the printed material and cause the liquid to be attached to the discharged material.
2. Description of the Related Art
An ink jet printer as an example of the liquid discharging apparatus will be described. The ink jet printer includes a serial printer which executes a printing job while causing a carriage having a printhead mounted thereon to reciprocate in the direction interesting the direction in which a paper is transported (see JP-A-2004-284209, JP-A-2005-81713, JP-A-2004-268337, JP-A-2006-96028, and JP-A-7-61084).
The ink jet printer of this type has a problem such that vertical rule marks are inclined when printing rule marks due to various causes described below. This problem means that an image is inclined, which is becoming more remarkable as the length of nozzle rows increases.
As a first cause of the inclination of the vertical rule mark, for example, there is a structural cause such that a printhead 13 is mounted on a carriage 10 in an inclined posture as shown in FIG. 5. The printhead 13 includes nozzle rows 31 including a plurality of nozzles 30, 30, . . . arranged along a transport direction A of a paper P. The printhead 13 is supposed to be mounted in such a manner that the nozzle rows 31 extend in parallel to the transport direction A which is orthogonal to a primary scanning direction B in which the carriage 10 moves. However, when the printhead 13 is mounted on the carriage 10 in an inclined posture, the nozzle rows 31 are also inclined with respect to the transport direction A of the paper P by an angle of inclination θ.
When a rule mark M (see FIG. 7) is printed on the paper P in this state, it is printed with an inclination of a, which is the same as the inclination of the nozzle rows 31, when the carriage 10 is moved at a very low velocity as shown in FIG. 8. However, when the carriage 10 is moved outward at a normal velocity, a velocity Vc1 of the carriage 10 is added and hence the rule mark M is printed with an inclination of b, and when the carriage 10 is moved homeward, a velocity Vc2 of the carriage is added and hence the rule mark M is printed with an inclination of c, so that the ink drop positions are displaced.
Subsequently, as a second cause of the inclination of the vertical rule mark, there is a structural cause such that ink discharge velocities Vn1, Vn2, and Vn3 are different from each other due to the difference in ink discharge positions d, e, and f of the respective nozzles 30 of the nozzle rows 31 of the printhead 13 among the downstream side, the center portion, and the upstream sides thereof as shown in FIG. 9. More specifically, as shown in the drawing, it is a case where the discharge velocity Vn is gradually lowered in the transport direction A of the paper P such that the ink discharge velocity Vn1 at the position d of the nozzles 30 on the downstream side is the highest, then is lowered to the ink discharge velocity Vn2 at the position e of the nozzles 30 in the center portion, and then to the ink discharge velocity Vn3 at the position f of the nozzle 30.
In this case, when ink drop distances H1, H2, and H3 between the nozzles 30 and the paper P are all the same irrespective of the ink discharge positions d, e, and f, the ink drop which is discharged from the position d of the nozzles 30 on the downstream side where the ink discharge velocity is the highest reaches the paper P at an earliest moment. Then, the ink drops from the position e of the nozzles 30 in the center portion reach the paper P next, and then from the position f of the nozzles 30 on the upstream side. The velocity of movement of the carriage 10 in the primary scanning direction B is added thereto, so that the inclination of the vertical rule mark is resulted. This inclination occurs in the opposite direction in the outward and homeward movements of the carriage.
As a third cause of the inclination of the vertical rule mark, there is a structural cause such that the ink drop distances H1, H2, and H3 are different depending on the difference of the ink discharge positions d, e, and f within the nozzle rows 31 of the printhead 13 as shown in FIGS. 10 and 11. More specifically, even though the ink discharge velocities Vn1, Vn2, and Vn3 from the respective ink discharge positions d, e, and f are the same, when the paper P is inclined to be higher on the downstream side in the transport direction A as shown in FIG. 10, or when the printhead 13 is inclined to be lower on the downstream side in the transport direction A as shown in FIG. 11, the ink drop from the position d of the nozzles 30 on the downstream side reaches the paper P at the earliest moment, then from the position e of the nozzles 30 in the center portion the ink drops, and then from the position f of the nozzles 30 on the upstream side as in the case shown in FIG. 9. The velocity of movement of the carriage 10 in the primary scanning direction B is added thereto, so that the inclination of the vertical rule mark is resulted as in the case of the second cause.
As a fourth cause of the inclination of the vertical rule mark, there is a fact that the ink discharge velocity is influenced by the resistance of the air as shown in FIG. 12. Accordingly, an initial discharge velocity Vn11 of the discharged ink is decreased gradually as the ink drop distance increases. In other words, the ink discharge velocity will be Vn11>Vn12>Vn13. Therefore, when the ink drop distance is increased according to the difference of the ink discharge positions d, e, and f of the nozzle rows 31 as the third cause, the ink drop positions in the primary scanning direction B of the carriage 10 is displaced depending on the difference of the ink drop distance due to the influence of gradual decrease in velocity. This displacement occurs in the opposite direction in the outward and homeward movements of the carriage.
As a fifth cause of the inclination of the vertical rule mark, there is a fact that the velocity component Vc11 of the carriage 10 in the ink discharge velocity is influenced by the resistance of the air as shown in FIG. 13. Accordingly, the velocity component Vc11 of the carriage 10 in the ink discharge velocity is decreased gradually as the ink drop distance increases. For example, the velocity component on the basis of the velocity Vc1 of the carriage in the outward movement will be Vc11>Vc12>Vc13. Therefore, when the ink drop distance is increased according to the difference of the ink discharge positions d, e, and f of the nozzle rows 31 as the third cause, the ink drop positions are displaced in the primary scanning direction B of the carriage 10 depending on the difference of the ink drop distance due to the influence of gradual decrease of the velocity component. This displacement occurs in the opposite direction between the outward and homeward movements of the carriage.
As a sixth cause of the inclination of the vertical rule mark, there is an influence of the flow of air C which is generated by the reciprocal movement of the carriage 10 in the substantially sealed space in the printer body 3 as shown in FIG. 14. When the air C flows between the nozzle rows 31 and the paper P, the ink drop positions on the paper P are displaced.
As a seventh cause of the inclination of the vertical rule mark, there is a “swing” caused by a supporting point Q as a connecting point between a toothed belt 11 and the carriage 10 from being apart from the center of gravity W of the carriage 10 having the printhead 13 mounted thereon as shown in FIG. 15. Since the carriage 10 swings and inclines in different directions by the reciprocal movement of the carriage 10, displacement of the position of the ink drop on the paper P occurs according to the direction of movement of the carriage 10.
However, although a technology to correct the inclination of the paper P with respect to the primary scanning direction B of the carriage 10 by rotating the paper P is disclosed in JP-A-2004-284209, it cannot be a countermeasure for the structural cause such as the first cause of the inclination of the vertical rule mark such that the printhead 13 is mounted on the carriage 10 in the inclined posture. When the configuration as disclosed in JP-A-2004-284209 is employed, the device is upsized, and hence a large space for installing the device is required. In addition, its advantage can hardly be expected for an elongated paper P.
Although a technology to make the inclination of the nozzle rows is adjustable by pressing a side surface of the printhead 13 by a pressing member is disclosed in JP-A-2005-81713, the first cause of the inclination of the vertical rule mark cannot be addressed with high degree of reliability. It is difficult to address the remaining second to seventh causes by the pressing member. The technology disclosed in JP-A-2004-268337 enables the provision of the supporting point Q of the carriage 10 in the vicinity of the center of gravity W of the carriage 10 by inclining the printhead 13 so as to be parallel to the paper P. However, the seventh cause of the inclination of the vertical rule mark cannot be addressed with high degree of reliability. The remaining first to sixth causes cannot be addressed at all.
In the same manner, the technology disclosed in JP-A-2006-96028 restrains the inclination of the carriage 10 by applying an urging force to a carriage guide shaft by a compression spring in the direction intersecting the axial line of the carriage guide shaft at a position apart from the center of gravity W in the primary scanning direction B on a plane horizontal to the paper P. However, the seventh cause of the inclination of the vertical rule mark cannot be addressed with high degree of reliability. The remaining first to sixth causes cannot be addressed at all. In addition, since the magnitude of the urging force is needed to increase as the acceleration of the carriage 10 increases, as the weight of the carriage 10 increases, and as the distance to the center of gravity W of the carriage 10 increases, an additional load is applied when reciprocating the carriage 10.
Although a technology disclosed in JP-A-7-61084 is adapted to eliminate rattling of the carriage 10 by forming the shape of extension of the belt for reciprocating the carriage 10 into a triangle shape, the seventh cause of the inclination of the vertical rule mark cannot be addressed with high degree of reliability. The remaining first to sixth causes cannot be addressed. Since extending the belt into a triangle shape requires a large space, upsizing of the device might be resulted.